At present the electrical power consumed by a client subscriber installation, supplied by the alternating-voltage grid, and the corresponding electrical power consumption, are determined from direct measurements of the physical parameters of the installation, such as the supply voltage, the intensity of the electric current delivered, the phase displacement between the electric current delivered and the supply voltage.
Usually electronic modules make it possible, on the basis of the aforementioned values of voltage, current and phase displacement, to calculate the active or reactive electrical power consumed, and, by integrating successive power values over a given time range, the electrical energy consumed.
The aforementioned electronic modules are most often installed in a meter, such as an electronic meter and can in certain cases proceed to transmission of the aforementioned measured values and/or of the values of power or of energy finally consumed.
The aforementioned meters are satisfactory.
However, they have the drawback that they require the aforementioned electronic modules to be installed in the meter itself, and therefore within the subscriber's private premises, i.e., most often, the subscriber's dwelling.
Various developments have been proposed for moving the measurement and metering of power or of energy away from the subscriber's private premises.
One such approach consists of carrying out measurement of supply voltage and of current delivered outside of the subscriber's private premises, by analysing the overall load curve of the installation either at the meter, or upstream of the latter, on the branching of the subscriber installation, with a view to employing non-intrusive processes, known as NIALM, for Non-Intrusive Appliance Load Monitoring.
The aforementioned non-intrusive processes are clearly of benefit for suppliers, distributors and consumers of electrical energy faced with the challenge of forecasting the costs of energy, of developments of networks and of reduction of consumptions.
The NIALM processes reveal several degrees of non-intrusion, those comprising a stage of automated training of the appliances, described in U.S. Pat. No. 4,858,141, and those comprising a stage of manual training of the appliances, described for example in U.S. Pat. No. 5,483,153. The manual NIALM processes prove to be more accurate than the automatic NIALM processes, as the consumption signatures of the appliances are collected at different states of consumption.
However, this semi-intrusion is annoying for the subscriber and unattractive for the distributor or supplier of electrical energy.
In the case of manual NIALM processes, a library of electrical receiving appliances is constructed, from an electric current sensor on each appliance.
In the case of automatic NIALM processes, a library of electrical receiving appliances, improving over time, is constructed based on the powers measured at the meter.
The aforementioned libraries actually make it possible to identify each electrical appliance and its consumption, and have promoted development towards identification of the usages of these appliances, or even of the habits, of usage or of consumption of the latter by subscribers provided with them.
Thus, various procedures have been proposed for identification of usages:                based on recognition of the variation in current intensity, as described in patent application FR 2 645 968. This variation is compared with a threshold representative of an event, connection or disconnection of a domestic load. The threshold values are listed in a library;        from measurement of the variations of active and reactive power and/or of admittance of the installation in the steady state, as described in U.S. Pat. No. 4,858,141. Comparison with a reference table of various appliances available on the market, stored in a library, is carried out;        from measurement of the current at the fundamental frequency and of its harmonics, as described in U.S. Pat. No. 6,816,078. Each appliance is identified by the harmonics (by frequency transform FFT) that it generates, and is classified in a library. The operation of the electrical appliances is evaluated at the true value by verification of the existence of the highest harmonic frequencies making up the total electric current;        from measurement of the active and reactive powers of the installation in transient conditions, as described in U.S. Pat. No. 5,483,153. The shapes of the transients are compared against a database for recognition of the loads;        based on exploitation of the start-up HF pulse emitted by electrical appliances connected to the electricity grid as described in patents EP 1 136 829 and U.S. Pat. No. 7,078,982 B2. This procedure requires, if necessary, on each appliance to be detected, fitting a device for emitting HF signals on the public network, receivers or repeaters for amplifying the HF signals. Although described as non-intrusive, this procedure requires several series of switching the electrical appliances on and off one after another, when the identification device is first installed;        based on measurements carried out on the current and voltage for determining the variation of the impedance of the loads of the installation over time, as described in patent application WO 93/04377. However, such a process is still intrusive. A bulk storage component in the meter must be replaced periodically by an employee.        
All of the aforementioned processes involve a level of intrusion that is incompatible with the mass diffusion represented by the vast numbers of domestic appliances.
The aforementioned processes make use of parameters and quantities that are more in keeping with grids supplying purely sinusoidal voltage, such as apparent, reactive, and active powers, effective values of current and of voltage, and are thus harmed, as they are poorly suited, to the wide use, on subscriber installations, of more and more numerous electronic appliances generating electrical perturbations and noise, which are superposed on the fundamental component.
The aforementioned processes that are best known by a person skilled in the art employ, for analysing the signals, frequency processing of the fast Fourier transform (FFT) type.
This type of processing requires a relatively large observation window of the signal being processed, in order to provide effective discrimination of the various components of the signal being processed, fundamental frequency, at 50 Hz or 60 Hz, and harmonic frequencies, for satisfactory processing of the aforementioned noise components superposed on the fundamental component.
In parallel with the aforementioned methods of purely frequency analysis, by frequency transform, of the Fourier transform type, other theoretical methods of analysis of the response, transmitted in real time, of systems submitted to a variable electromagnetic field have been proposed.
Developed essentially for studying the response of reflectors or of antennas excited by an electromagnetic wave that is assumed to propagate by plane waves, a special method, called the Pencil Method, was proposed, which makes it possible, from the transient and permanent response of a target to radiated electromagnetic excitation, to determine the poles and residues of the aforementioned response by resolving a generalized eigenvalue problem.
For a description of a theoretical approach of the aforementioned Pencil method, applied to a target formed by an electrically conducting wire, we may usefully refer to the article with the title “Generalized Pencil-of-Function Method for Extracting Poles of an EM System from its Transient Response” published by Yingbo Hua and Tapan K. Sarkar, members of the Department of Electrical and Computer Engineering, Syracuse University, Syracuse, N.Y. 13344-1240, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 37, No. 3, February 1989, p 229-234.
More recently, a comparative study between the comparative performance in spectral resolution between the frequency processing techniques, such as the Fourier transform, and the Pencil method, with the title “Comparison between the Matrix Pencil Method and the Fourier Transform Technique for High Resolution Spectral Estimation” published by Jose Enrique Fernandez del Rio and Tapan K. Sarkar, Department of Electrical and Computer Engineering, 121 Link Hall, Syracuse University, Syracuse, N.Y. 13244-1240, Digital Signal Processing 6, 108-125 (1996) Article No. 0011, showed that the Pencil method is superior to the frequency processing methods by Fourier transform, with respect to dispersion of estimation and root-mean-square error, for a signal-to-noise ratio above a certain threshold value.